1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to circuit interrupter electronic trip units configurable through a plurality of adjustable switches. The invention also pertains to systems including circuit interrupter electronic trip units.
2. Background Information
Electrical switching apparatus such as circuit interrupters and, in particular, circuit breakers of the molded case variety, are well known in the art. See, for example, U.S. Pat. No. 5,341,191.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. Molded case circuit breakers typically include a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the case or automatically in response to an overcurrent condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open and close the separable contacts, and a trip unit, which senses overcurrent conditions in an automatic mode of operation. Upon sensing an overcurrent condition, the trip unit trips the operating mechanism to a trip state, which moves the separable contacts to their open position.
Industrial circuit breakers often use a circuit breaker frame, which houses a trip unit. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271. The trip unit may be modular and may be replaced, in order to alter the electrical properties of the circuit breaker.
It is well known to employ trip units which utilize a microprocessor to detect various types of overcurrent trip conditions and to provide various protection functions, such as, for example, a long delay trip, a short delay trip, an instantaneous trip, and/or a ground fault trip. The long delay trip function protects the load served by the protected electrical system from overloads and/or overcurrents. The short delay trip function can be used to coordinate tripping of downstream circuit breakers in a hierarchy of circuit breakers. The instantaneous trip function protects the electrical conductors to which the circuit breaker is connected from damaging overcurrent conditions, such as short circuits. As implied, the ground fault trip function protects the electrical system from faults to ground.
Each circuit breaker is designed for a specific maximum continuous current. This current rating may be set by a suitable selection mechanism, such as by a rotary switch or by selection of a resistor (e.g., a “rating plug”) which converts a current to a voltage for use by the trip unit. In some instances, a single circuit breaker frame may be easily adapted for installations which call for a range of maximum continuous currents, up to the design limits of the frame, through use of the selection mechanism by which the current rating of the device can be established. Typically, the pick-up currents for the various protection functions have been selectable multiples or fractions of this current rating. Thus, instantaneous protection trips the device any time the current reaches a selected multiple of the rated current, such as, for example, ten times the rated current. Pick-up for short delay protection is a lesser multiple of the rated current, while pick-up current for long delay protection may be a fraction of the rated current. Typically, the short delay trip is only generated when the short delay pick-up current is exceeded for a short delay time interval, although, in some applications, an inverse time function is also used for short delay protection.
Currently, many electronic trip units use adjustable (e.g., without limitation, rotary) switches to vary functional trip settings, such as, for example and without limitation, long delay pickup (Ir), long delay time (LDT), short delay pickup (SDPU), ground fault pickup (GFPU), and short delay time and ground fault time (SDT/GFT). The adjustable switches are typically labeled on a per unit basis and are common to all current sensor (e.g., current transformer) types. The Ir adjustable switch is based upon a percentage of the current sensor. For example, the Ir adjustable switch has eight positions. The lowest position represents 40% of the current sensor rating and the highest position corresponds to 100% of the current sensor rating.
Manufacturers of circuit interrupters readily seek to reduce the size and cost of circuit interrupters and electronic trip units. Hence, it is desirable to maintain the full functionality of an electronic trip unit while reducing its cost. It is also desirable to eliminate components of an electronic trip unit while also maintaining all its functions.
It is known to display individual trip curves on a computer monitor where the curve can be adjusted.
It is also known to download circuit breaker parameter values from a remote computer using network or serial communications. This potentially reduces the human errors associated with inserting the correct parameter values in the correct circuit breaker.
U.S. Pat. No. 6,005,757 discloses a microprocessor-based trip unit in which a microcomputer and transceiver communicate with another trip unit to acquire the predetermined settings of the other trip unit. The microcomputer includes a firmware routine which employs the acquired predetermined settings as its own predetermined values.
There is room for improvement in systems including circuit interrupter trip units.